The present invention generally relates to a wafer chuck used in a semiconductor process chamber and more particularly, relates to a wafer chuck in a semiconductor process chamber that is capable of producing an inert gas blanket for insulating a wafer from harmful chemicals and a method for using the chuck.
In the fabrication of semiconductor devices, a silicon wafer must be process by many processing steps, i.e. as many as several hundred, in order to produce a final product of an IC chip. In the various chemical or physical processes for performing the fabrication steps, a silicon wafer must be held onto a wafer carrying device, such as a wafer chuck securely in a process chamber such that an active surface of the wafer can be processed.
One or more of such numerous processing steps may be an etching or cleaning step in which a silicon wafer is etched in a spin etcher. In a typical spin etcher, a wafer is held on a wafer chuck that rotates at a predetermined rotational speed while an acid solution is sprayed on top of the wafer surface. For instance, in recent semiconductor processing technology, cobalt deposition is frequently used in forming transistor gates on the silicon surface. After the completion of a cobalt deposition process, the backside of the wafer must be cleaned due to the extreme mobility of the cobalt atoms during a sputtering process. A suitable cleaning process for removing the cobalt particles on the backside of a silicon wafer is by using the spin etching apparatus.
Many different types of spin etchers have been designed to suit specific etching requirements on a silicon wafer. FIG. 1 illustrates a conventional spin etcher that has four-level etch chambers or etch stations formed in a single etcher.
Referring now to FIG. 1, wherein a conventional multi-leveled spin etcher 10 is shown. Spin etcher 10 is constructed by four different levels of reaction chambers 12, 14, 16 and 18. Each of the reaction chambers are formed by a partitioning member 20 which cooperates with a wafer chuck 22 divides the cavity of the spin etcher in four different sub-cavities 22, 24, 26 and 28. The conventional wafer chuck 22 is provided with an internal passageway 30 for passing an inert gas such as nitrogen into a cavity 32 formed between a wafer 34 and the top surface 36 of the wafer chuck 22. The wafer 34 is supported by a plurality of mounting pins 38 as shown in FIG. 1. The wafer chuck 22 is driven, or rotated, by shaft 40 to a suitable rotational speed during the etching process.
The multi-leveled spin etcher 10 shown in FIG. 1 provides the benefit that a single etcher can be used to execute various etching steps by either using different etchant or the same etchant at different concentrations. During the etching process, an acid, or a diluted acid solution, is sprayed from the top of the chamber (not shown) to etch the backside of the wafer 34, for instance, after a silicon wafer is sputter deposited with cobalt. The shaft 40 elevates or lowers the wafer chuck 22 between the various etch stations 12, 14, 16 and 18. The rotation of the shaft 40 and the rotation of the wafer 34 situated on top of the wafer chuck 22 results in a more uniform etch reaction on the surface of the wafer, and thus a more satisfactory etch reaction.
In most spin etching reactions, a highly corrosive acid in a diluted form is sprayed into the chamber cavity 22, 24, 26 or 28. While each of the chamber sub-cavities 22xcx9c28 is equipped with an exhaust conduit 42 to evacuate the sub-cavities after an etch reaction has been conducted, such withdrawal is not always effective such that residual acid vapor stays in the sub-cavities. In the multi-leveled spin etcher 10, the upward/downward movement of the wafer chuck 22 further contributes to the migration of acid vapor from one sub-cavity into the sub-cavity above it. The acidic vapor therefore corrodes the backside of the wafer 34 by flowing into the cavity 32 formed between the wafer and the wafer chuck 22. In the case of a backside cleaning after a cobalt deposition on a silicon wafer, the backside of the wafer 34, i.e. the side that faces downwardly, is actually the active side of the wafer and thus, any corrosive effect on the active side of the wafer can produce detrimental effects. When the active surface of the wafer 34 is attacked by acid vapor, serious quality and reliability problems occur which greatly effects the throughput of the spin etching process.
It is therefore an object of the present invention to provide a wafer chuck in a semiconductor process chamber that can be used without the drawbacks or shortcomings of the conventional wafer chuck.
It is another object of the present invention to provide a wafer chuck for use in a semiconductor process chamber capable of producing an inert gas blanket shielding a wafer positioned thereon.
It is a further object of the present invention to provide a wafer chuck for use in a semiconductor process chamber that is equipped with inert gas passageways in the chuck for flowing an inert gas into an upper portion of the reaction chamber and forming an inert gas blanket.
It is another further object of the present invention to provide a wafer chuck for use in a semiconductor process chamber that is provided with a plurality of apertures in a sidewall of the wafer chuck for flowing an inert gas into the reaction chamber and thus insulate a wafer positioned on the chuck.
It is still another object of the present invention to provide a process chamber for processing semiconductor wafers that includes a wafer chuck capable of producing an inert gas blanket around a wafer positioned on the chuck and preventing the wafer from being damaged by residual chemical vapor in the chamber.
It is yet another object of the present invention to provide a process chamber for processing semiconductor wafers which is equipped with a multi-leveled sub-chamber for etching a semiconductor wafer and protecting the wafer from being damaged by residual chemical vapor in the process chamber.
It is still another further object of the present invention to provide a method for chemical treating a wafer topside without damaging the wafer backside by residual chemical vapor in a process chamber.
It is yet another further object of the present invention to provide a method for chemical treating a wafer topside without damaging the wafer backside by residual chemical vapor in a process chamber by providing a wafer chuck equipped with internal passageways for feeding an inert gas into the chamber cavity and thus blocking the wafer from the residual chemical vapor.
In accordance with the present invention, a wafer chuck for producing an inert gas blanket to insulate a wafer positioned on the chuck and a method for chemical treating a wafer topside without damaging the wafer backside by residual chemical vapor in the chamber are provided.
In a preferred embodiment, a method for chemical treating a wafer topside without damaging the wafer backside by residual chemical vapor in a process chamber can be carried out by the operating steps of first providing a wafer chuck for mounting a wafer thereon; positioning the wafer chuck in the process chamber wherein an upper surface of the chuck substantially separates an upper chamber and a lower chamber; and rotating the chuck and conducting a chemical process on the topside of the wafer while simultaneously flowing an inert gas through a sidewall of the wafer chuck into an upper portion of the lower chamber stopping chemical vapor from flowing from the lower chamber into the upper chamber and preventing the backside of the wafer from being attacked by the chemical vapor.
The method for chemical treating a wafer topside without damaging the wafer backside by residual chemical vapor in the process chamber may further include the steps of stopping a flow of the chemical into the upper chamber and withdrawing residual chemical from the upper chamber while the inert gas being flown into the lower chamber. The method may further include the step of mounting a wafer chuck in a process chamber that is a spin etcher, or the step of providing the process chamber in a multi-level spin etcher. The method may further include the step of rotating the wafer chuck to a rotational speed between about 500 RPM and about 1200 RPM, or the step of flowing an inert gas of N2 into the upper portion of the lower chamber. The method may further include the step of mounting a wafer onto a plurality of mounting pins in the upper surface of the wafer chuck such that the wafer is suspended over and spaced-apart from the upper surface, or the step of purging an inert gas onto the wafer backside during the rotation of the chuck and the chemical process is conducted on the wafer topside. The method may further include the step of moving the chuck upwardly or downwardly to each of a plurality of sub-chambers in the multi-level spin etcher, or the step of providing inert gas nozzles through the sidewall of the wafer chuck.
The present invention is further directed to a wafer chuck for producing an inert gas blanket to insulate a wafer positioned thereon in a process chamber which includes a body portion in an inversed cylindrical shape that has an upper surface larger than a lower surface, the upper surface has a size capable of dividing a cavity of the process chamber into an upper chamber and a lower chamber; a plurality of mounting pins in the upper surface of the body portion adapted for supporting a wafer thereon suspended from the upper surface; a plurality of apertures in the upper surface for flowing an inert gas into a cavity formed between the wafer and the upper surface; a shaft portion attached to the body portion for providing a rotational motion to the body portion; and a plurality of apertures in a sidewall of the body portion for flowing an inert gas into the lower chamber forming an inert gas blanket blocking a passageway between the upper and the lower chambers.
In the wafer chuck for producing an inert gas blanket to insulate a wafer positioned thereon in a process chamber, the process chamber may be a spin etcher or a multi-level spin etcher. The wafer chuck may further include a partition means mounted on a chamber wall cooperating with the upper surface of the chuck body to substantially divide an upper chamber from a lower chamber. The wafer chuck may further include means for rotating the shaft portion to a rotational speed between about 500 RPM and about 1200 RPM.
The present invention is still further directed to a process chamber for processing semiconductor wafers that includes a wafer chuck formed of a body portion and a shaft portion, the body portion has an upper surface of sufficient size to divide a cavity in the chamber into an upper cavity and a lower cavity, the upper surface of the body portion has a plurality of apertures for purging an inert gas onto a backside of a wafer positioned thereon; a plurality of apertures in a sidewall of the body portion of the wafer chuck for flowing an inert gas into an upper portion of the lower cavity forming an inert gas blanket insulating the wafer; a partition means mounted to a chamber wall of the chamber cooperating with the upper surface of the body portion to form the upper and lower cavities; and a motor means for rotating the shaft portion to a rotational speed between about 500 RPM and about 1200 RPM.
The process chamber for processing semiconductor wafers may further include conduit means in the body portion of the wafer chuck for transporting an inert gas to the plurality of apertures in the upper surface and in the sidewall of the body portion. The process chamber may be a multi-level spin etcher. The inert gas flown through the plurality of apertures may be nitrogen or argon. The process chamber may further include a plurality of mounting pins in the upper surface of the body portion for supporting a wafer thereon and for suspending the wafer from the upper surface.